1. Field of the Invention
The present invention relates to a centrifugal multiblade fan which includes a plurality of blades located around a rotation axis.
2. Description of the Related Art
Conventionally, in this kind of the centrifugal multiblade fan, a leading edge (an edge on the rotation axis side) of each blade is formed into a smooth curved shape in cross section to reduce a separation of airflow at the leading edge on some level, and reduces a fan efficiency reduction and a noise generation caused by the separation.
However, when the leading edge of each blade is formed into the smooth curved shape in cross section, a point where the airflow separates and a point where the airflow reattaches are temporally fluctuated. Therefore, the airflow between the blades becomes unstable. As a result, the fan efficiency is reduced and the noise is generated.
A centrifugal multiblade fan that can reduce the separation of the airflow is described in JP-A-2002-168194, for example. In this centrifugal multiblade fan, a tumor having a similar shape as that of a separation area of the airflow is provided at a back surface of each blade. The back surface of each blade is a surface on the side opposite to a rotation direction of the centrifugal multiblade fan, and a ventral surface of each blade is an opposite surface of the back surface.
In this way, the centrifugal multiblade fan according to JP-A-2002-168194 reduces a space where the separation of the airflow generates from the back surface of each blade, and reduces the noise generation caused by the separation.
However, the point where the airflow separates and the point where the airflow reattaches are temporally fluctuated. Furthermore, the tumor is difficult to be completely the same shape as that of the separation area of the airflow. Therefore, the space where the separation of the airflow generates cannot be reduced enough.